Approach protective apparatus



July 29, 1947. A. L. BROWNLEE APPROACH PROTECTIVE APYARA'I'US 4 She ets-Sheet 1 Filbd Oct. 26, 1942 A. l... BROWNLEE APPROACH PROTECTIVE AYPARATUS Filed 001;. 26, 1942 July 29,1941.

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. Q@ 99 kESbm @E Q MQ @E wwbm IN V EN TOR. gllarzlfimwalee Patented July 29, 1947 UNITED s'rA'rE APPROACH rno'rao'rrvic APPARATUS Allan L. Brownlce, Itasca, Ill. I Application October 26, 1942, Serial No. 463,314 y My-invention relates, generally, to detecting apparatus and it has particular relation to'apparatus for detecting the presence of a foreign body such as a trespasser on property where the presence of such persons is forbidden.

It has been proposed in the past to employ a change in the dielectric characteristic between two charged electrodes caused by the introduction of a foreign body such as a trespasser for indicating the presence of such trespasser. In general, such systems have comprised an electrode which is insulated from ground and constitutes one plate of a capacitor. The other plate of the capacitor is the ground. A source of high voltage alternating current is connected between the electrode and ground for maintaining the necessary difference of potential. Various means have been suggested formeas-uring the difference in the character of the dielectric between the electrode and ground dueto the presence of a foreign body therebetween. I

An important disadvantage of such systems has been that they are adversely affected by change in weather conditions and it has been necessary to resort to complicated and inefficient means for overcoming this difficulty. The principal disadvantage resides'in the fact that the electrode is insulated from ground and that thisinsulation constitutes a major portion of the dielectric between the electrode and ground. Now when this insulation is subjected to rain, sleet or snow conditions, it is changed materially and consequently the calibration of the apparatus is correspondingly affected although no foreign body is present which the apparatus is intended to detect. i

In view of the foregoing it is an object of my invention to provide for detecting the presence of a foreign body such as a trespasser on property out of doors regardless of the weather conditions that may exist.

Another object of my invention is to provide for automatically compensating for changes in weather conditionswhich might otherwise adversely affect apparatus for detecting the presence of a foreign body such as a trespasser on property a from which entrance by the public is forbidden.

Other objects of my invention will, in part, be obvious and in part appear hereinafter.

For a more complete understanding of the nature andscope of my invention reference can be had to the followingdetailed description taken in connection with the accompanying drawings in which: 1

Figure 1 illustrates, diagrammatically, the

fundamental features of my invention; a p

Claims. (cl. 177-352) Figure-2 is a view,

tion of my invention to. the protection of property;

Figure 3 illustrates, diagrammatically, .the man I ner in which the elements making up the invention can be extended for enlarging the scope of further modifications of 'myinvention.

Referring now particularly to Figure 1 of the drawings, it will beobserved that the reference character I0 designates, generally, a transformer having a primary winding II that is'arranged to.

be energized from a suitable source l2 of alternating current. The source I2 is employed to represent the conventional alternating current source which maybe of the order'of or 240 volts, or any other suitable source, as will be readily understood. The transformer I!) also includes a secondary winding l3 which is arranged to operate at a relatively high voltage such 'as 5000 volts between its terminals I4 and 15.

A mid-tap I6 is provided between the terminals l4 and I5 and it is arranged to be grounded, as illustrated. It will be understood then thatonehalf of the voltage of the secondary winding [3 appears between the terminal I4 and the mid-tap l6 and that the other half appears between the mid-tap i6 and the terminal 15. It ,will be understood that other voltages than 5000 volts can be used if desired without departing from the spirit and scope of this invention.

Connected to the terminals l4 and I5 of the secondary winding I3 are electrodes l8gand l9 which are mounted in insulated spaced relation by insulators 20 and 2I-, as shown. The insulators 20 and 2| are carried by suitable supports 22 and 23, each of which is grounded, as illustrated. As will hereinafter appear, the electrodes 18 and I9 may be mounted on alternate fence posts which take the place of the supports 22 and 23. The electrodes l8 and I9 may be in the form of bare conductors. However, it is preferable for the sake of safety to enclose the electrodes l8 and I0 in suitable insulation.

Located symmetrically between the electrodes [8 and I9, is a detector electrode 25 which iscarried on insulators 26 that are supported by a suitable support 21 which, as shown, is grounded.

It will be understood that the detector electrode partly in perspective and partly diagrammatic, showing a. typical applica-- suitable electro-static shield 23 which prevents the detector 23 from being aiiected by extraneous influences and makes it responsive solely to current flow between the detector electrode 25 and ground. The detector 23 may be or any suitable character, such as an electronic detector which will measure the flow of current between the detector electrode 25 and ground. It may be arranged to operate suitable signalling means or other apparatus to give an alarm under certain predetermined conditions which will be set forth hereinafter.

The detector electrode 25 i located with respect to the electrodes l3 and I3 so that the electro-static capacity as represented by the capacitor 33 in broken lines between the electrodes l3 and 25 is substantially equal to the electrostatic capacity represented by the capacitor 3b in broken lines between the electrodes 25 and I3. Thus a balanced condition exists between the electrodes l3 and 25 and 25 and I3 and consequently no current flows through the detector 23.

, Preferably, the electrodes l3 and I3 are spaced about twenty feet apart. with the detector electrode 25 midway therebetween or about ten feet from each electrode l3 and I3. Now, it a foreign body, such as a trespasser, approaches the space between the electrodes l3 and 25, for example, the character of the dielectric therebetween is changed and the previously maintained balance is upset. Consequently, current flows through the detector 28 in an amount which depends upon the character of the change. A suitable alarm i given in response to the change in current flow as measured by the detector 23 and appropriate steps may then be taken as the situation may warrant.

Because oi the symmetrical relationship of the detector electrode 25 with respect to the electrodes l8 and IS, the operation of the system is unaffected by changes in weather conditions.

I pacitors 34 and 35 may vary depen ing upon weather conditions and other conditions. The

capacitance of these circuits may be the same orelectrodes l3 and and 25am! l3insuchman-' nerthatthebalanceisnotupset. Itwillbeob- For example, the presence or rain, sleet or snow will affect the character of the dielectric between the electrodes i8 and 25 and 25 and IS in substantially the same manner so that there will be no resultant difference in these dielectrics and consequently there will be no change in the current flow as measured by the detector 23.

The capacitance of the electrode i3 to ground can be represented by the capacitor 32 shown in broken lines. In like manner the capacitance of the electrode IE! to ground can be represented by the capacitor 33 shown in broken lines. The capacitance of capacitors 32 and 33 will change depending upon the character of the insulators 23 and 2| under different conditions. For example, when the weather is dry the eflective dielectric for the capacitors 32 and 33 will be relatively high. Under adverse weather conditions when the insulators 20 and 2| are wet, their dielectric value is correspondingly reduced. These changes may or may not be identical for the capacitors 32 and 33. However, this makes no difference in the operation of the system in view of the fact that whatever current may iiow through the circuit represented by the capacitors 32 and 33 does not flow through the detector 23 and consequently it is unaffected.

The capacitance between the electrode l3 and the secondary winding l3 can be represented by the capacitor 34 shown in broken lines. Likewise, the capacitance between the electrode l5 and the capacitor 35 also shown in broken lines. The caviousthattheoccurrenceoisuchsconditicnis extremely unlikely and ordinarily this may be disregarded. However, it it is desired to provide for this eventuality then the secondary winding llcanbegroundedetapointotherthanthemidtap i3. Pbrexampleitcanbegroundedltsn oil-center tap as indicated by the tap 33. The detector 25 can then bendiusted to take care of this slight unbalance. Alternatively, thedetectorelectrode25canbelocatedslishflyunsymrfietrically with respect to the electrodes II 8nd I It will be obvious that the system shown in Pigurelanddescribedhereinbeiorelsnotsiiected by changes in frequency 0! the source I2. I! it shouldoccurthatthesystemislikelytobesi- 'iected by an adjacent power circuit operating at a conventional frequency, such as 60 cycles per second, then a higher frequency can be employed for thesource 12, such as 130 or 240 cycles per second and a suitable filter can be provided in the circuit to the detector 23 so that it will be responsive only to frequencies above 60 cycles.

In Figure 2 of the drawings there is shown a section oi a fence to which the present invention has been applied. It will be observed that electrodes 33 and 33 are carried by insulators 43 and 3| which are mounted on ienc'e posts 32 and 53. A detector electrode 35 is mounted on insulators :5 that are carried by an intermediate fence post As shown in Figure 3 of the drawings several pairs of electrodes 33 and 33 are provided with a detector electrode 35 for each pair and located midway the electrodes making up each pair. The number of pairs of electrodes 33 and 33 and the number of detector electrodes 35 will be governed by the particular conditions involved. In a particular installation involving aience 01' 2,200 feet in length, the installation would be divided into twenty foot sections and duplicate apparatus would be installed for each section.

As shown in Figures 2 and 3 of the drawings conductors 50 and 5| are provided for interconnecting the electrodes 33 and 33, respectively. The conductors 53 and 5| can be mounted in any suitable manner such as on support arms 52 carried by the fence posts 32, 33 and 41, as shown. The conductors 53 and 5| can be connected to the terminals I5 and I5 of the secondary winding II of the transformer I previously described.

Each of the detector electrodes 55 can be provided with its own detector 23 and shield 23. as shown in Figure 2. However, it may be desirable to connect allot the detector electrodes 55 of one section together, as shown in Figure 3, and then to connect them to the detector equipment. When the system shown in Figure 3 is used it is desirable to extend the shield from the detecting equipment to each of the detector electrodes 35. When an individual detector 23 is employed for each of the detector eelctrodes 55, it is unnecespacitance oi these circuits as represented by ca- 73 sary to use such extensive shielding, it being nechigh voltage secondary winding I3.

-essary only to extend the shielding from each de- However, the arrangement of the electrodes with respect to the detector electrode is different.

It will be observed that a. pair of electrodes 55 and 51 is provided. These electrodes can be in the form of wires and are connected for energization to the terminals l5 and I5 of the high voltage secondary winding l3, as shown. The electrode 55 is carried by insulators 58 on supports 55 which are grounded. The electrode 51 is likewise carried by insulators 58 which are mounted on grounded supports 5|. It will \be observed that the electrodes 55and 51 extend in opposite directions.

Below the electrodes 55 and 51 and in parallel spaced relation with respect thereto is a detector electrode 52. The detector electrode 52 is carried by insulators 55 that may be mounted, as shown, on the supports 55 and 5|. Thedetector is connected between the detector electrode 52 and ground.

The capacitance between electrode 55 and the detector electrode 52 can be illustrated by the capacitor 54 shown in broken lines. Likewise, the capacitance between the electrode 51 and the detector electrode 52 can be illustrated by the capacitor 55 also shown vin broken lines. Now, under normal operating conditions the capacitance of capacitor 55 substantially equals the capacitance of capacitor 55. Because of this'no potential exists between the detector electrode 52 and ground and consequently no current flows through the detector 28.

When this symmetrical capacitance relationship is disturbed, as by the presence of a foreign body between either the electrode 55 and detector electrode 52 or between the electrode 51 and the detector electrode 52, this symmetrical capacitance relationship will no longer obtain. As the result current will flow to ground through the detector 28 which will be measured thereby.

A suitable alarm then can be given as will be readily understood.

In the system shown in Figure 4 stray currents through stray capacitance to ground are local to the transformer and do not affect the detector 28. Capacitance between the detector electrode 52 and 'ground in parallel with the detector 28' merely affects its sensitivity but not its function in detectingthe unbalance which may exist between the capacitors 54 and 55 as I described.

In Figure 5 of the drawings there is illustrated, diagrammatically, still another embodiment of the invention. It will be observed that the same transformer I8 is employed, as previously described, having a primary winding ll energized from a source l2 ofalternating current and a Likewise, the same detector 28 and shield 29 are employed.

In'the construction shown in Figure 5 electrodes 68 and 58are provided and are connected, as shownyto the terminals II and I5 of the high voltage secondary winding IS. The elecor similar conductors and are disposed in transposed insulated relationship in a substantially vertical plane. The electrodes 58 and 58 are carried by suitable insulators 18 on suitable sup-.

ports H which are grounded. A detector electrode 12 is carried by insulators 13 on thefsupports H and is located in spaced relationship to and in the same plane as the electrodes 58 and 58.. The detector 281s connected between the detector electrode I2 and ground, as shown.

The arrangement of the electrodes 58 and is such that the capacitance represented by the sum of the capacitance of capacitors l5 and I1, shown in broken lines, between the electrode 58 and the detector electrode 12 is equal to the sum of the capacitance ofv the capacitors I8 and 18,.

of any of the capacitors l5, 11, I8 or 18, this balanced condition will be disturbed and current will flow through the detector 28. This may be caused by the presence of a foreign body between the portions of the electrodes 58 and58 adjacent the detector electrode 12. A suitable signal can then be given as to the presence of the foreign body and necessary action can be taken.

As in the systems described hereinbefore, the

detector 28 is unafiected becauseof the flow of stray currents through stray capacitanceto ground from the high voltage secondary winding l3. Also, the flow of current through capacitance to ground from the detector electrode merely affects the sensitivity of the detector 28.

It will be obvious that many changes can be made in the foregoing system without departing from the spirit and scope of thepresent invention. Therefore, it is intended that all matter shown in the accompanying drawings and described hereinbefore shall be interpreted as illustrative and not in a limitin sense.

Iclaim as my invention:

1. Apparatus for detectingthe presence of foreign bodies out of doors in various kinds. of weather conditions comprising, in combination, a transformer-having a primary winding connected to a source of alternating current and a relatively high voltage secondary winding having a center tap connected to ground, a pair of electrostatic main electrodes in insulated spaced relation energized from said transformer by connection to the terminals of said secondary winding, an electrostatic detector electrode insulated from ground and electrostatically substantially symmetrically disposed with respect to said pair of electrodes, and detector means connected at one side to said detector electrode and connected at the other side through ground to said center tap of the transformer secondary winding where-, by substantially no current flows through said detector means under normal operating conditions,

and whereby substantially no current flows through said detector means when leakage occurs trodes 58 and' 59 may be in the form of wires .75 substantially disturbs said electrostatic symmetry.

2. Apparatus for detecting the presence oi-ioreign bodies out oi doors in various kinds of weather conditions comprising, in combination, a transformer having a primary winding connected to a source of alternating current and a relatively high voltage secondary winding having a center tap connected to ground, a pair of electrostatic main electrodes energized from said transformer by connection to the terminals of said secondary winding; insulator means ior each main electrode for supporting the same out or doors in spaced relation, grounded support means for said insulator means, an electrostatic detector electrode and insulator means for supporting the same out 01' doors and symmetrically with respect to the electrodes of said pair, grounded support means for the last named insulator means, and detector means connected at one side to said detector electrode and connected at the other side through ground to said center tsp of the secondary winding, whereby substantially no current flows through said detector means under normal operating conditions and whereby substantially no current flows through said detector means when leakage occurs across said first named insulatormeans between said main electrodes and ground because such leakage current is bypassed around said detector means through ground to said center tap, but whereby substantial current is caused to flow through said detector means when a foreign body gets between either of said main electrodes and said detector electrode.

3. Apparatus for detecting the presence of for-- eign bodies out of doors in various kinds of weathmeans for the last named insulator means, detector means connected between said detector electrode and ground-tor measuring the current flow therebetween, the point of connection oi said detector means with said secondary winding through ground and the relative spacing between said detector electrode and said main electrodes being so related to each other that substantially no current flows through said detector means under normal operating conditions but current does flow through said detector means when a foreignbocbygetsbetweeneitherotsaidmainelem nation, a transformer having a primary winding for connection to an alternating current source and a relatively high voltage secondary winding having a tap intermediate its terminals, a plurali ity of pairs oi electrodes mounted in insulated er conditions comprising, in combination, a transformer having a primary winding adapted to be connected to a source of alternating current and a relatively high voltage secondary winding having a tap intermediate its terminals adapted to be connected to ground, a pair of main electrodes 7 adapted to be energized from said transformer by connection to said terminals of said secondary winding, insulator means for each main electrodefor supporting the same out of doors in spaced relation, grounded support means for said insulator means, a detector electrode, insulator means for said detector 'electrode for supporting the same out of doors between said main electrodes, grounded support means for the last named insulator means, and detector means connected at one side to said detector electrode and connected at the other side to said intermediate tap through ground for measuring the change in current flow therebetween due only to the presence of a foreign body between either of said electrodes of said pair and said detector electrode.

4. Apparatus for detecting the presence of foreign bodies out of doors in various kinds of weather conditions comprising, in combination, a transformer having a primary winding adapted to be connected to a source of alternating current and a relatively high voltage secondary winding having an intermediate tap adapted to be connected to ground, a pair of main electrostatic electrodes adapted to be energized from said transformer by connection to the terminals of said-secondary winding, insulator means {or each,

main electrode for supporting the same out of doors in spaced relation, grounded support means for said insulator means, a detector electrostatic electrode and insulator means for supporting the same out 0! doors and symmetrically with respaced relation with corresponding electrodes 01' each pair connected together and for energization to the terminals of said secondary winding, a detector electrode disposed between each of said pairs of electrodes, and detector means connected between said detector electrodes and said tap of said secondary winding for measuring the flow of current therebetween due only to the presence.

0! a foreign body between one oi the electrodes of said pairs of electrodes and the associated detector electrode. s

6. Apparatus for detecting the presence of ioreign bodies out of doors in various kinds oi weather conditions comprising, in combination, a transformer having a primary winding adapted to be connected to a source of alternating current and a relatively high voltage secondary winding having a center tap adapted to be connected to ground, a pair 01' main electrostatic electrodes in insulated spaced relation and extending in opposite directions and adapted to be energized from said transformer by connection to the terminals of said secondary winding, a detector electrostatic electrode insulated i'rom ground and extending in parallel spaced relation relative to said pair of main electrodes whereby the capacitance between each electrode of said pair and said detector electrode is substantially the same, and detector means connected between said detector electrode and ground for measuring the current flow therebetween when a foreign body substantially changes the capacitance between one of said main electrodes and said detector electrode, there being substantially no current flow through said detector means as long as the capacitance between each'main electrode and said detector electrode remains substantially the same.

7. Apparatus for detecting the presence of iorground, a pair 01' electrodes in insulated transposed relation in a plane adapted to be energized spect to said main electrodes, grounded support 7| from said transiormer by connection to the terminals of said secondary winding, adetector electrode in the plane of and in parallel spaced relation with respect to said pair of electrodes and insulated from ground whereby the capacitance between each electrode of said pair and said detector electrode is substantially the same, and detector means connected between said detector electrode and ground for measuring the current flow therebetween when a foreign body substantially changes the capacitance between one of said electrodes of said pair and said detector electrode, there being substantially no current flow through said detector means as long as the capacitance between each electrode of said pair and said detector electrode remains substantially the same.

8. An alarm system comprising three independent electrical conducting wires extending over an area, the approach to which is to be guarded,

means for electrically energizing two of said wires providing dual capacitance to the third wire, ar-

ranged and dimensioned to be substantially proportionally aflected by normal weather changes, detector means, including alarm means, operatively connected between said third wire and ground having electrical characteristics maintaining said alarm means unoperated during normal weather changes, substantially proportionally affecting the capacitance of said two ener' gized wires to said third wire, and operating said means unoperated during normal weather changes substantially proportionally afiecting the capacitance of said two energized wires to said third wire, and operating said detector means when the capacitance of said two energized wires to said third wire are non-proportionately affected as by the approach of a foreign object to said wires.

10. An alarmsystem comprising three independent electrical conducting wires extending over an' area, the approach to which is to be guarded, a transformer having a primary winding adapted to be connected to a source of alternating current and a relatively high voltage secondary winding having an intermediate tap adapted to be connected to ground, the terminals of said secondary winding being connected to two of said wires, such energization of said two wires providing dual capacitance to the third wire, arranged and dimensioned to be substantially proportionally affected by normal weather changes, detector means connected between said alarm means when the capacitance of said twoenergized wires to said third wire are non-proportionately aflected as by the approach of a foreign object to said wires.

9. An alarm system comprising three independent electrical conducting wires extending over an area, the approach to which is to be guarded, means providing a source of high voltage alternating current connected across two or said wires and having a connection intermediate the connections to said two energized wires, the energizaticn of said two latter wires providing dual capacitance to the third wire, arranged and dimensioned to be substantially proportionally afiectedby normal weather changes, and detector means connected between said third wire and said intermediate connection of said source having electrical characteristics maintaining said detector third wire and ground having electrical characteristics maintaining said detector means unoperated during normal Weather changes substantially proportionally affecting the capacitance of said two energized wires to said third wire, and

operating said detector means when the capaci-' tance of said two energized wires to said third wire are non-proportionately afiected as by the approach of a foreign object to said wires.

' ALLAN L. BROWNLEE.

REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Number Name Date 2,147,748 Luck et a1. Feb. 21, 1939 1,375,414; Osborne Apr. 19, 1921 2,097,760 Failla Nov. 2, 1937 FOREIGN PATENTS Number Country Date 284,307 Great Britain Jan. 29, 1929 346,061 Great Britain Apr. 9, 1931 

